Atomic force microscope for small samples having dual-mode operating capability

Abstract

This invention is a dual mode atomic force microscope which has significant advantages for small samples. The major point of novelty of this device is the provision for mounting samples onto the deflection mechanism, thereby allowing the tip to be separately mounted. The invention therefore allows for increased flexibility in the design of the tip, which can improve the performance of the microscope. The main configuration and several tip designs and variations of the deflection mechanism and the sample holder are described. Also, methods for using a microscope of this type are presented. The invention primarily consists of an AFM where the sample is mounted on the cantilever arm, and the tip is mounted separately, not on the cantilever arm. The cantilever arm and sample are scanned relative to the sample either by moving the sample or by moving the tip. Dual mode operation is achieved by combining cantilever arm deflection measurement by optical means with, for example, detection of a current between the tip and sample.

Wherefore, having thus described the present invention, what is claimed is: 
     
       1. An atomic force microscope useful for scanning small samples to obtain the surface topography and other surface information of a surface thereof, comprising: a cantilever arm supported on one end for movement on an opposite end, said opposite end having a sample holding area thereon carrying a sample to be scanned, said cantilever arm being removably held by a structural member of the atomic force microscope;   a scanning tip;   scanning means disposed over said sample holding area and carrying said scanning tip on a scanning end thereof for moving said scanning tip over said sample in a scanning pattern;   detector means for detecting movement of said opposite end of said cantilever arm and for developing a signal at an output thereof reflecting an amount of movement of said opposite end of said cantilever arm;   controller and driver means connected to said scanning means and to receive said signal from said detector means for driving said scanning means in said scanning pattern and for deriving surface image data from said signal;   wherein:   said cantilever arm is held by a removable mounting block;   said structural member is adapted to removable receive a plurality of mounting blocks containing individual cantilever arms with samples thereon for scanning at a plurality of scanning stations; and,   said scanning tip is positionable over respective ones of said scanning stations.   
     
     
       2. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of a sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the improvement for selectively operating the atomic force microscope in either or both of dual modes comprising: first detector means for detecting movement of the opposite end of the cantilever arm and for developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   means for applying a bias voltage between the scanning tip and the sample;   second detector means for detecting a current between the scanning tip and the sample and for developing a second signal at an output thereof indicative of the amount of said current; and,   controller and logic means for generating surface data from said first signal and for generating supplemental surface data from said second signal;   wherein the scanning means moves the scanning tip over the surface of the sample in a scanning pattern comprising a plurality of adjacent scan lines and wherein additionally:   said controller and logic means includes means for employing said first signal on alternate ones of the scan lines whereby at that time the scanning probe microscope operates as an atomic force microscope and for employing said second signal on the remaining ones of the scan lines whereby at that time the scanning probe microscope operates as a scanning tunneling microscope.   
     
     
       3. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of a sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the improvement for selectively operating the atomic force microscope in either or both of dual modes comprising: first detector means for detecting movement of the opposite end of the cantilever arm and for developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   means for applying a bias voltage between the scanning tip and the sample;   second detector means for detecting a current between the scanning tip and the sample and for developing a second signal at an output thereof indicative of the amount of said current; and,   controller and logic means for generating surface data from said first signal and for generating supplemental surface data from said second signal;   wherein the scanning means moves the scanning tip over the surface of the sample in a scanning pattern comprising a plurality of adjacent scan lines and wherein additionally:   said controller and logic means includes means for employing said first signal while scanning the scan lines in one direction whereby at that time the scanning probe microscope operates as an atomic force microscope and for employing said second signal while scanning the scan lines in an opposite direction whereby at that time the scanning probe microscope operates as a scanning tunneling microscope.   
     
     
       4. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of a sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the improvement for selectively operating the atomic force microscope in either or both of dual modes comprising: first detector means for detecting movement of the opposite end of the cantilever arm and for developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   means for applying a bias voltage between the scanning tip and the sample;   second detector means for detecting a current between the scanning tip and the sample and for developing a second signal at an output thereof indicative of the amount of said current; and,   controller and logic means for generating surface data from said first signal and for generating supplemental surface data from said second signal;   wherein the microscope is primarily employed as a scanning tunneling microscope and additionally including for the protection of the scanning tip:   said controller and logic means including means for monitoring said first signal and for controlling the scanning tip with said first signal whenever said first signal exceeds a pre-established threshold whereby damage to the scanning tip from being forced into the surface of the sample as a function of said second signal at insulating areas of the surface of the sample being scanned is prevented.   
     
     
       5. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of the sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the method of selectively operating the atomic force microscope in either or both of dual modes comprising the steps of: detecting movement of the opposite end of the cantilever arm and developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   applying a bias voltage between the scanning tip and the sample;   detecting a current between the scanning tip and the sample and developing a second signal at an output thereof indicative of the amount of the current; and,   generating surface topography data from the first signal and generating supplemental surface data from the second signal;   wherein the scanning means moves the scanning tip over the surface of the sample in a scanning pattern comprising a plurality of adjacent scan lines and additionally including the steps of:   employing the first signal on alternate ones of the scan lines whereby at that time the scanning probe microscope operates as an atomic force microscope; and,   employing the second signal on the remaining ones of the scan lines whereby at that time the scanning probe microscope operates as a scanning tunneling microscope.   
     
     
       6. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of the sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the method of selectively operating the atomic force microscope in either or both of dual modes comprising the steps of: detecting movement of the opposite end of the cantilever arm and developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   applying a bias voltage between the scanning tip and the sample;   detecting a current between the scanning tip and the sample and developing a second signal at an output thereof indicative of the amount of the current; and,   generating surface topography data from the first signal and generating supplemental surface data from the second signal;   wherein the scanning means moves the scanning tip over the surface of the sample in a scanning pattern comprising a plurality of adjacent scan lines and additionally including the steps of:   employing the first signal while scanning the scan lines in one direction whereby at that time the scanning probe microscope operates as an atomic force microscope; and,   employing the second signal while scanning the scan lines in an opposite direction whereby at that time the scanning probe microscope operates as a scanning tunneling microscope.   
     
     
       7. In a scanning probe microscope having a scanning tip, scanning means for causing movement of the scanning tip over a surface of the sample in a scanning pattern, and a cantilever arm supported on one end for movement on an opposite end relative to characteristics of the surface of the sample, the method of selectively operating the atomic force microscope in either or both of dual modes comprising the steps of: detecting movement of the opposite end of the cantilever arm and developing a first signal at an output thereof indicative of the amount of movement of the opposite end of the cantilever arm;   applying a bias voltage between the scanning tip and the sample;   detecting a current between the scanning tip and the sample and developing a second signal at an output thereof indicative of the amount of the current; and,   generating surface topography data from the first signal and generating supplemental surface data from the second signal;   wherein the microscope is primarily employed as a scanning tunneling microscope and for the protection of the scanning tip additionally including the step of:   monitoring the first signal and controlling the scanning tip with the first signal whenever the first signal exceeds a pre-established threshold whereby damage to the scanning tip from being forced into the surface of the sample as a function of the second signal at insulating areas of the surface of the sample being scanned is prevented.